Phase shift spectra of a fiber-microsphere system at the single photon level

Akira Tanaka, Takeshi Asai, Kiyota Toubaru, Hideaki Takashima, Masazumi Fujiwara, Ryo Okamoto, Shigeki Takeuchi

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


We succeeded in measuring phase shift spectra of a microsphere cavity coupled with a tapered fiber using a weak coherent probe light at the single photon level. We utilized a tapered fiber with almost no depolarization and constructed a very stable phase shift measurement scheme based on polarization analysis using photon counting. Using a very weak probe light ( n̄ = 0.41), we succeeded in observing the transition in the phase shift spectrum between undercoupling and overcoupling (at gap distances of 500 and 100 nm, respectively). We also used quantum state tomography to obtain a 'purity spectrum'. Even in the overcoupling regime, the average purity was 0.982±0.024 (minimum purity: 0.892), suggesting that the coherence of the fiber-microsphere system was well preserved. Based on these results, we believe this system is applicable to quantum phase gates using single light emitters such as diamond nitrogen vacancy centers.

Original languageEnglish
Pages (from-to)2278-2285
Number of pages8
JournalOptics Express
Issue number3
Publication statusPublished - Jan 31 2011
Externally publishedYes

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics


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